1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a program for, in particular, processing a tomographic image of a subject's eye (i.e. an eye to be examined).
2. Description of the Related Art
A tomographic imaging apparatus such as an OCT (Optical Coherence Tomography) apparatus can three-dimensionally observe a state in a retinal layer of an eye. In recent years, the tomographic imaging apparatus has been highlighted because it is useful to perform more accurately a diagnosis of a disease. As a form of the OCT, there is a TD-OCT (Time Domain OCT) in which a light source with a wide bandwidth and a Michelson interferometer are used. The TD-OCT is constructed in such a manner that by scanning a delay of a reference arm, interference light with backward scattered light of a signal arm is measured and information of depth decomposition is obtained. However, it is difficult to obtain a high-speed image using TD-OCT because a plurality of A-scans have to be combined to give a B-scan, a plurality of which have to be combined to give the 3-D tomographic image, and this consecutive scanning process takes time. Therefore, as a method of obtaining an image at a higher speed, an SD-OCT (Spectral Domain OCT) has been known as an OCT for obtaining an interferogram by a spectroscope by using a light source with a wide bandwidth. In this method, Fourier transforms are used to interpret images that can be taken all at once rather than as individual scans, thus saving time over the TD-OCT. An SS-OCT (Swept Source OCT) is a method of measuring a spectral interference using a photodetector of a single light channel and using a high-speed wavelength sweep light source as a light source.
In this instance, if a form change of a retina in a tomographic image can be measured, a degree of progress of a disease such as glaucoma or the like and a degree of recovery after a treatment can be quantitatively diagnosed. In order to quantitatively measure such form changes of the retina, such a technique that boundaries among layers of the retina are detected from a tomographic image by using a computer and a thickness of layer is measured has been disclosed in Japanese Patent Application Laid-Open No. 2008-073099A. A technique for measuring a thickness of choroid (coat membrane) has also been disclosed in Japanese Patent Application Laid-Open No. 2011-072716 for the purpose of diagnosing early glaucoma.